Electric discharge device



y 23, 1961 A. J. HUMPHREY ETAL 2,985,786

ELECTRIC DISHARGE DEVICE Filed Feb. 12, 1959 FIG.|

VOLTS ARC DROP LOAD CURRENT E INKEflgORS ANDR WJ. U WILLIAM A- MANELECTRIC DISCHARGE DEVICE Andrew J. Humphrey, Cleveland, and William A.Maijala, Burton, Ohio, assignors to The Reliance Electric andEngineering Company Filed Feb. 12, 1959, Ser. No. 792,901

4 Claims. (Cl. 313-187) The invention relates in general to electricdischarge devices and more particularly to thermionic gas or vaporelectric discharge devices.

Two types of gaseous discharge devices are used as rectifiers and gridcontrolled rectifiers. One type employs a heated emissive surface as acathode and another type employs an arc cathode. This invention dealsprimarily with the heated cathode type of device or the general class ofhot cathode gas filled rectifying devices, which may also be used asconverting devices, but hereinafter referred to as rectifying devices.One characteristic of a thermionic gas discharge device is the increasein the voltage drop through the device during conduction when theeffects of tube aging show up. These effects may be due to a lesseningof the inert gas filling of the device, reduction in the emission of thecathode due to deterioration from ion bombardment or through the usingup of the emissive coating or perhaps from physical damage due to misuseof the tube. This voltage between elements during conduction isdetermined by all these factors. This increased voltage drop or are dropseriously limits the normal useful life of the device, because itincreases the watts loss and heating in the device, and lowers itsefficiency.

Accordingly, an object of the invention is to provide a means toindicate approaching end of life of the device.

Another object of the invention is to provide a primary medium and asupplemental medium within an electron discharge device.

Another object of the invention is to provide a supplemental gas orvapor in a device and having a higher ionization potential than theprimary gas or vapor therein.

Another object of the invention is to provide a means for establishing adifferent radiation spectrum upon aging of an electron discharge device.

Still another object of the invention is to provide an electrondischarge device with a primary gas or vapor having a definite radiationspectrum and also providing a supplemental gas or vapor of a higherionization potential which increasingly ionizes as the arc drop withinthe device increases to indicate approaching end. of life of the device.r

Another object'of the invention is to utilize,.in an electric dischargedevice, a supplemental gas of a smaller percentage than the primarymedium, and of a higher ionization potential to radiate a differentspectrum upon aging, together with a more rugged cathode to withstandion bombardment.

Other objects and a fuller understanding of this in vention may be hadby referring to the following description and claims, taken inconjunction with the acoompanying drawing, in which:

Figure 1 is a diagram of volts versus current indicating variousoperational curves of the electron discharge device;

Figure 2 is a diagrammatic showing of a gas or vapor electric rectifierdevice incorporating the invention; and

Figure 3 is a modified rectifier device'incorporatingi the invention.

Patented May 23, 1 951,

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electron discharge devices and in the rectifier or converter class ofgas or vapor filled devices there are at least two common types in usetoday. One is a device having a fillant in the envelope of xenon and theother one having a fillant of mercury plus an inert gas. This inert gasmight be either argon or xenon in present day rectifier devices. Thissecond type of thermionic device usually contains a small pool of liquidmercury to furnish the mercury vapor atmosphere and the pressure thereofis established in accordance with the physical considerations of thedevice and the amount of cooling. In such prior art devices the inertgas was generally included in the fillant primarily to allow operationwhen mercury pressure was low due to adverse temperature conditions. Inthe xenon filled prior art devices one method by which end of usefullife could occur was by the occlusion of the fillant on the walls and inthe structure of the tube. Since the fillant is an inert gas, chemicalcombination does not occur but the gas when ionized can, under certainconditions of operation, achieve a velocity which will drive the ioninto the solid portions of the tube with such force that it is diflicultfor the molecule to be released. When this occurs the gas is said toclean up. This clean up effect is essentially limited to ions althoughnonionized molecules may occasionally be driven into the walls.

Another cause of depletion of the fillant in the xenon tube issputtering. In this action an ion having a high velocity will knock offa portion of the anode or grid or some other solid portion of the tubeand this metal will be sputtered on to the surface of some other portionof the tube. When this occurs gas ions or molecules are sometimestrapped between the sputtered metal and the element upon which it issputtered. This also results in removal of the useful gas in the tube.As a result of occlusion and sputtering, the available ionizable mediumor fillant becomes less; hence, the pressure is reduced and theionization potential necessary for satisfactory operation of the devicebecomes greater.

In all the gas or-vapor filled thermionic cathode discharge devices, nomatter what the primary fillant may be, life may be limited by otherfactors as well. As previously stated, the emission of electrons fromthe cathode may be reduced. This may occur in several ways, one of whichis deterioration of the electron emissive material, which is generallymerely a coating on a base metal. Any misuse of the device, accidentalor otherwise, such as overcurrent, overheating, overvoltage, arc-backsand the like, all may damage the cathode emitting surface. All of theseaging factors tend to raise the arc drop or voltage drop across thedevice. This rising arc drop is an unavoidable characteristic of aging,and is utilized in this invention as an indicator of approaching end oflife.

The are drop is the entire drop in voltage between the cathode and anodeof the device, and is used to ionize the gas or vapor medium. As theelectrons are accelerated from .the cathode toward the anode, theyionize the molecules of the fillant, and this ionization neutralizes thespace charge which otherwise would exist near the tube elements, as itdoes in a so-called vacuum tube'or device. In, operation of such gas orvapor devices, there is found in the vicinity of the electrodes a glowcharacteristic of the ions carrying current. While light is a. secondaryproduct in these rectifier devices, it is necessarily present.

The particular voltage and current under which a gaseous rectifier orthyratron is required to operate will determine the physical spacingbetween elements and the pressure of the gas fillants in the device.Ordinarily if a rectifier is filled with a gas having a high ionizationpotential, the addition of even trace amounts of a lower ionizing gaswill decrease the arc drop markedly and will also decrease the voltagewhich the device will hold off between elements. The filling of the gaswith the lower ionization potential will essentially determine thevoltage which can be. sustained between elements and the arc drop.Addition of a gas with a higher ionization potential will have verylittle effect upon the ability of the tube to Withstand voltage and uponarc drop. As long as the amount of this supplemental gas is between and70% of the primary gas, its effects are negligible. Above thisproportion some effect on tube operating characteristics can be noted.These effects may not be undesirable for particular types of rectifyingdevices hence the amount of the supplemental fillant may be considerablyabove that of the primary fillant.

The amount of the fillant in a discharge device determines the pressuretherein. If a high voltage device is required, only a small amount offillant, e.g. at a pressure of microns of mercury, is used. The lowpressure enables the device to withstand the high voltage, both forwardand backward, yet the scarcity of molecules of gas limit the currentcarrying capacity materially, considering the physical size of thedevice. Conversely, if higher current capacities are required, then moregas molecules and hence higher fillant pressures must be used, whichinherently lower the voltage rating of the device. The end result is acompromise of as little gas as one can get by with for a particularcurrent rating in order to meet a desired voltage rating.

The prior art also used mixtures of inert gases or a mixture of vaporsuch as mercury and inert gases to achieve lower ionization potential ofthe fillant. This was used for three different reasons; namely, for aidin starting of the device, for improved operation, or for lowtemperature operation. Additionally, in gaseous discharge devices usedas lamps, the mixtures of gases were used to achieve an initialdesirable color of the discharge.

The present invention relates to the use of an additional orsupplemental gas or vapor for the purpose of indicating approaching endof life of the device. The primary gas or vapor may still be that whichhas been formerly used; for example, xenon, or mercury plus an inertgas, such as xenon, argon or krypton. The supplemental gas or vaporadded in accordance with this invention is, one which has a higherionization potential and an easily detectable different radiationspectrum from that of the primary fillant.

The supplemental gas of this invention is chosen as neon, because of itseasily detectable red glow upon ionization, and because its ionizationpotential of about 22 volts is satisfactorily materially higher than theionization potential of the commonly used primary fillants. Mercury hasan ionization potential of about 10 volts, and xenon has an ionizationpotential of about 12 volts; therefore, a prefererd mixture is the useof xenon as the primary fillant at a pressure of approximately 110microns of mercury, and a supplemental gas of neon at a pressure ofabout 60 microns of mercury. Thus during normal operation of the deviceand during normal life of the device the arc drop or discharge throughthe device is sustained by the primary fillant of xenon with this aredrop being about 12 volts through the xenon. As the tube or device ages,primarily through the occlusion of the primary fillant, the arc droptends to rise. As it approaches 22 volts in arc drop the neonsupplemental gas will commence to glow. This will cause a characteristicred color of discharge which will be quite distinct from the dischargeof xenon which has a violet cast. In the typical glass envelopedischarge device this may readily be noticed on observation by untrainedpersonnel, thus signifying that the tube has reached approximately theend of normal life and should be replaced. If a metal envelope dischargedevice is used it may be provided with a transparent window to observethe change in radiation A second choice of fillant for electrondischarge devices is a primary fillant of. mercury plus an inert gassuch as xenon, krypton or argon or a combination thereof with the inertgas having a pressure sufficient to allow a degree of operation when themercury pressure as determined by the physical characteristics of thedevice and the amount of cooling would be quite low. This inert gasadditive is preferably xenon at a pressure in the order of 60 microns ofmercury. The supplemental gas would be neon at a pressure of 50 to. 70microns of mercury. In this mixture of fillants the device would have anarc drop of about 10 volts, as determined by the mercury or the lowionizing. potential inert gases and after the ionization potential ofthe neon was gradually approached during life of the device the neonwould gradually begin to be ionized and to radiate its characteristicred glow.

A third choice of fillants of the invention is the use of mercury as aprimary fillant and neon as a supplemental gas. In this case the neonpreferably has a pressure of approximately microns of mercury.

A fourth choice of fillant mixture is a primary gas or vapor of mercuryplus argon with the argon being at a pressure of about 60 microns ofmercury. The supplemental gas is neon at a pressure of about 50 to 70microns of mercury. The argon has an ionization potential of about 16volts; hence, the discharge of the device is primarily through themercury vapor at about 10 volts arc drop with the argon normally notionizing and sustaining the discharge except at low temperatureoperation. Again as end of life of the device approaches the neon willincreasingly ionize to radiate its characteristic red glow.

In the preferred fillant described above of xenon plus neon variousmixtures have been tried and it has been found that the neon at apressure of about 60 microns of mercury is quite satisfactory. Ten andfifteen microns of mercury pressure of the neon have been tried but havebeen found to be insufficient. Thirty five microns of mercury pressureof neon has been tried and the characteristic neon red glow shows upquite well to indicate approaching end of life of the device. If toomuch neon is included, this tends to lower the ability of the device towithstand the operating potential applied on the anode and cathode;hence, the voltage rating of the device is reduced. Also, if too littlexenon is included in the device this harms the satisfactory operation ofthe device primarily because of lack of current carrying capacity andlife.

Figure 1 shows a characteristic operational curve 11 of volts versusamperage. This is a typical are drop within the device between cathodeand anode for different load currents passed by the device. Line 12indicates approximately the rated current of the device which isdesigned to utilize the device to approximately its maximumcapabilities. This curve 11 shows that normally a device hasapproximately a 10 volt arc drop through the range of rated current andthat this are drop only increases where the rated current of the deviceis exceeded. Curve 13 is a curve of the operational characteristicsafter the tube or device has aged considerably and curve 14 is anoperational curve with still further aging. These curves show that theare drop or voltage drop in the discharge increases considerably in thehigher current ranges as the tube ages. As stated above, this is causedprimarily by occlusion of the gas or vapor which reduces the totalamount of gas or vapor available and ionizable to carry the are ordischarge; hence, the potential required to ionize the remaining fillantincreases. With the preferred mixture of xenon and neon the neon beginsto glow at about point 15 on curve 13 when the ionization potential ofabout 22 volts has been reached on this curve 13. The device maycontinue to be used, of course, dependent on circuit considerations,however, the characteristic red glow of the device indicates that thearc drop within the device haemcreased materially and; hence, theefliciency has been likewise materially reduced. This red glow indicatesthat the device should be replaced for etficient operation, and toprevent further deterioration and complete breakdown.

Figure 2 shows diagrammatically a gas or vapor electric rectifier device18 which may take any number of forms and the present drawing is only byway of illustration of one form of the invention. This rectifier device18 includes a transparent envelope 19 to contain the primary andsupplemental fillants. This envelope contains the elements necessary tomake the rectifier device such as an anode 20, a gird 21 and a cathode22.

Figure 3 shows a modified rectifier device 24 which is made of metal,and, hence, opaque. In this case a transparent window 25 is provided ina suitable location in the wall of the rectifier device 24 in order toobserve the color of the radiation from the gas or vapor within thedevice 24.

Cathodes of thermionic tubes are subject to sputtering when bombardedwith ions above a certain energy level. The cathode commonly used in agas thyratron is the barium oxide cathode and its damage point isbetween 20 and 30 volts arc drop. The so-called nickelate cathode willbe undamaged at are drops below 40 to 50 volts and is preferable for theindicating tubes of this invention using neon, which must operate on theindicating gas for an appreciable length of time before the tube isreplaced.

A nickelate cathode may be one wherein the electron emissive cathode hasa core of one of the metals adjacent to the iron group in the atomicseries of elements and on this core there is dissolved an electronemissive compound which comprises one of the metals chromium, manganese,copper and molybdenum, an alkaline earth metal and oxygen. Morespecifically, the electron emissive cathode may comprise a nickel corewith a barium nickelate dissolved therein and having additional bariumnickelate forming a spongy surface therefor.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of the circuit and thecombination and arrangement of circuit elements may be resorted towithout departing from the spirit and the scope of the invention ashereinafter claimed.

What is claimed is:

1. In a gas electric rectifier device, the provision of a primary gas ofXenon at a pressure in the order of 110 microns of mercury, and asupplemental gas of neon having a higher ionization potential than thatof I said primary gas and at a lower pressure in the order of microns ofmercury.

2. In a gas electric rectifier device, the provision of a primary gas ofxenon at a pressure in the order of microns of mercury, a supplementalgas of neon having a higher ionization potential than that of saidprimary gas and at a lower pressure in the order of 60 microns ofmercury, and a cathode in said device having an electron emissivesurface including a nickelate compound.

3. In a gas electric rectifier device, the provision of a primary gas ofxenon at a given pressure and a supplemental gas of neon having a higherionization potential than that of said primary gas and at a lowerpressure in the order of half said given pressure.

4. In an electric rectifier device, the provision of a primary mediumconsisting essentially of xenon sustaining the discharge therewithinthroughout the normal life of said device, supplemental gas meansconsisting essentially of neon and in the order of 10 to 50 percent ofthe total fillant pressure and having a higher ionization potential thanthat of said primary medium, whereby during normal life the discharge isthrough the primary medium and as aging raises the arc drop thesupplemental gas means increasingly ionizes and emits detectableradiation to indicate approaching end of life of said device, and atransparent portion in the envelope of said device.

References Cited in the file of this patent UNITED STATES PATENTSAnderson Dec. 13, 1955

